Appropriate charger for 24v 7Ah SLA battery?

[92saturnsl2]

I bought my youngest son a new Polaris RZR look-a-like ride-on toy today and am questioning the best way to charge the battery on it. I have always heard/read that the included brick chargers (chinese junk) are bad for the batteries and overcharge them, resulting in a short life, in the 3-5 month range and with generally poor performance over that time.

I looked at the electrical layout and it's a 24V 7Ah sealed lead acid battery. The charger is a 24v 1000mA brick unit, has a red/green charge indicator so appears to be somewhat of a smart charger in that it turns itself off (hopefully), but I still don't put a whole lot of faith into it. It connects through a standard size barrel plug and is wired directly to the battery with no intervening electronics.

I am wondering if my Noco Genius 7200 would work on it-- it has a 24v 3.6 amp setting but only has modes for "normal lead acid" and "cold/AGM" at that voltage. I'm not sure if or how the charging requirements of a sealed lead acid battery (similar to what you find in a computer UPS) differ from a standard lead acid or AGM type. Or if a 0.5C charging rate would be okay on these types of batteries. Perhaps there's something out there specifically for these types of batteries I should look into. Curious what you guys think...

 

[MrMoody]

That battery is almost certainly AGM, most likely 2 low quality 12V "1270" types assembled into a pack. The Noco would work fine on AGM mode, and won't cook it like the brick would. These type batteries generally recommend no more than .4C initial current, however. .5C may shorten the life some, but not nearly as badly as the brick would IMO. After it dies, which will probably take a year or more without the brick killing it, you can take the pack apart and replace them with 2 name brand 12V 9Ah ones of the same size that can be had for about $25 each.

 

[92saturnsl2]

I actually disassembled the "pack" which consisted of a plastic housing containing wires, resettable fuse, and a single 24v battery that is perhaps 1.5x the size of the 1270 12v battery you mention.

I expected to find two cheap 12v batteries in series too. That is what I will likely replace this one with when it bites the dust.

It just dawned on me I hadn't searched for a datasheet which might be available online and provide useful info like max charge rate. I simply popped the model number into Google to look into availability which didn't look good.

 

[thastinger]

I would assume it is a sealed lead acid battery as that would be the least cost per unit to produce. I can't imagine that it will have a run time longer than an hour and sounds like it would be getting a .7C rate from the charger so that should be ok.

 

[wrcsixeight]

Most of the Asian made inexpensive AGM batteries have a max 'recommended' charge rate of around 30% the battery capacity. The max amperage charge rate for 'cyclic' use is often stated right on the battery itself

I have a Ub 12180 battery, an 18 Ah AGm battery, it says no more than 5.4 amps.

That said, I have depleted it well below 50% and applied a 40 amp charger set to 14.7v and no mushroom cloud, and no noticeable heating of it in 5 minutes. After 5 minutes I lowered the potential to keep it under 10 amps. I'd not do this every single recharge though.

I am not familiar with too many 24v chargers. If I had to charge a small 24v battery pack that I did not want to separate into two 12v batteries to charge individually, I would likely use the 150 watt DC boost converter I own just because it was under 3$. It will go up as high as 31 volts under load. I recently used it to charge a 18v nicad and 24v nicad battery pack, but one needs to be there to disconnect nicads once they warm up.

An AGM battery can be determined to be full when it accepts ~0.5% of its rated capacity when held at absorption voltage (14.4 to 14.9v)

Such a boost converter hooked directly to a smart chargers output will likely not work as the smart charger will not see it it attached to a battery. The smart charger will need to be connected to a separate battery and the boost converter attached to that battery and then one can boost voltages upto the 28.8v range required for a 24v AGM battery. One could also just deplete the large enough 12v battery via the booster and then charge the 12v battery with their regular charger but this will cycle the larger 12v battery to some degree which is not always desirable.

They have 400 and 600 watt versions that ship from inside the US for more $$, the link below is just the cheapest 150 watt example slow boat from chine I happened to have linked. It is what I own. i have placed a 60mm computer fan bridging the heatsinks.

https://www.ebay.com/itm/150W-DC-DC-Boost-Converter-10-32V-to-12-35V-6A-Step-Up-Voltage-Charger-Power-AT/292409304867?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20160323102634%26meid%3D7657913fc82649e9be4524ee63d8b39d%26pid%3D100623%26rk%3D3%26rkt%3D6%26mehot%3Dpp%26sd%3D202692780913%26itm%3D292409304867%26pg%3D2047675&_trksid=p2047675.c100623.m-1

If the 7Ah of 24 batteries are well depleted they can likely exceed 150 watts of acceptance when initially hooked up if the voltage is set to 28.8v unloaded. One could set voltage to just above battery voltage and slowly raise it upto 28.8v over time to keep the load under the 150 watts.

My 150 watt booster with teh 60mm fan, passed nearly 200watts for a few to several minutes, when i did not monitor the 24v nicad battery pack close enough for heating, and it started going into thermal runaway.

I bring this up as while lead acid batteries are harder to get going into thermal runaway, the booster method linked above needs to be monitored and to decide as to when to remove the charging source, an Ammeter is required. When ampos taper to 0.5 amps oer 100Ah of battery capacity at 14.7v9for a 12v battery, remove charger. If amps start rising again before this amperage threshold is attained, remove charger.

My UB12180 will sometimes taper to 0.5% of capacity at absorption voltage, other times it will not.